The present invention relates to web decurlers for removing curl from a running web, and more particularly, to a web decurler for removing curl from a running web without changing the web register between web processing operations located on the upstream and downstream sides of the decurler.
Generally webs are stored in tightly wound rolls before they are processed. Sometimes they are re-rolled in between web processing operations. Such storage imparts a curl to the web, and particularly webs made from stiffer materials such as, for example, paper board used to make milk cartons.
It has been recognized by those working in this art that webs should be decurled, especially when the last web processing operation includes cutting the web into sheets or the like. If a web has not been decurled, or properly decurled, difficulty may be experienced in stacking the cut, free sheets. For example, if the remaining curl imparts a clockwise, or downwardly facing curve, to the sheets as they are cut, the leading edge of a sheet has a tendency to "catch" on the trailing edge of the preceding sheet as they are stacked. If the sheets have a counter-clockwise, or upwardly facing curve, the sheets have a tendency to "fly" when being stacked even to the extent of flying off the stacking table.
Prior web decurlers have attempted to remove the curl from running webs by passing the running web, in series, about the peripheral surfaces of a first relatively larger diameter roller, a second relatively smaller diameter roller and then a third relatively larger diameter roller. The three rollers are disposed in a generally triangular arrangement, with the central longitudinal axis of the relatively smaller diameter roller being offset to one side or the other, from a plane which includes the central longitudinal axes of the relatively larger diameter rollers.
In some of the prior decurlers, the relatively smaller diameter roller could be moved with respect to the plane of the relatively larger diameter rollers. Such movement of the relatively small diameter roller changed the amount that the running web was wrapped about the outer peripheral surfaces of the three rollers and thus the degree of curl that could be removed from the running web. The relatively smaller diameter roller could also be positioned on one side or the other of the plane including the central longitudinal axes of the relatively larger diameter rollers so as to remove selectively either clockwise or counter-clockwise curl from the running web.
Such movement of the relatively smaller diameter roller in these prior decurlers, however, changed the length of the web path through the decurler. This change in the web path caused problems in maintaining web registration between web processing operations located upstream and downstream of the decurler. Electrical compensating systems have been proposed and used to attempt to maintain web registration in such decurlers. Their usage has not been particularly successful and has increased the costs to the decurling operation.